The behavioral and neuroendocrine effects of various peripheral hormones, including the gonadal steroids, thyroid hormone(s), and anterior pituitary hormones, have been described by many investigators. Nevertheless little data exists on the precise neurochemical mechanisms mediating hormone-CNS interactions. Furthermone, despite the thorough characterization of hormone receptor(s) in the CNS over the past 10 years, these is virtually no understanding of how hormones interact physiologically with neurons. Studies in our laboratory have been desiqned to study the biochemical effects of hormones on neuronal preparations in vitro in an attempt to identify direct neurochemical effects on excitable tissue. Studies thus far have shown significant effects of biologically active estrogens on catecholamine efflux from the isolated hypothalamus in vitro. These effects were concentration dependent and not observed with biologically inactive estrogens such as estradiol-17alpha. These results suggest that estrogen may facilitate the release of catecholamines from the hypothalamus.